[pax]

Пример:

private GameObject pickedGO = null;
    public float distance;

    public void Update()
    {
        if(Input.GetMouseButtonDown(0))
        {
            if(pickedGO!= null)
            {
                Throw(pickedGO);
                pickedGO = null;
            }
            else
            {

                var distToPickedObject = float.MaxValue;
                GameObject picked = null;
                foreach (var obj in GameObject.FindGameObjectsWithTag("tk"))
                {
                    var dist = Vector3.Distance(obj.transform.position, transform.position);
                    if(dist<distToPickedObject)
                    {
                        distToPickedObject = dist;
                        picked = obj;
                    }
                }

                if (picked != null && distToPickedObject <= distance)
                {
                    PickUp(picked);
                    pickedGO = picked;
                }
            }
        }
    } 


функции Throw и PickUp надо создать самостоятельно для обработки бросания и подбора объекта соответственно.